Interconnection inverter devices for interconnecting with an alternating-current power system include a smoothing unit for stabilizing a voltage of input direct-current power. The smoothing unit has conventionally been configured by using an electrolytic capacitor for high power.
On the one hand, among interconnection inverter devices in which the direct-current power is an output of a solar cell, an interconnection inverter device with a high-voltage specification, such that an input voltage reaches even 700 VDC, requires a product with a high-breakdown voltage of about 850 WV (working voltage) allowing for derating as a breakdown voltage of an electrolytic capacitor for smoothing.
However, the electrolytic capacitor with such a high-breakdown voltage is not common in terms of its cost and configuration, and it is, therefore, difficult to be adopted into home electric appliances. Based on this background, the high-breakdown voltage is ensured in the interconnection inverter devices each with a high-voltage specification by serially connecting low-cost, high-availability two general-purpose electrolytic capacitors of about 450 WV or 500 WV.
There are few documents, related to the interconnection inverter device, which directly disclose measures against problems for this type of electrolytic capacitors. This is because it is thought common that circuit operation of a converter circuit or of an inverter circuit is directly stopped as safety measures upon device malfunction.
On the other hand, there is Patent document 1 as follows as a document which discloses not safety measures for protecting the device but safety measures for persons handling the device.
The Patent document 1 takes up the problem such that a service person may get a shock under a condition as follows, and discloses an interconnection inverter device as measures against the problem. The condition is such that he/she may get a shock upon operation of a detection function for preventing the device from being destroyed caused by overvoltage or overcurrent occurring inside the interconnection inverter device, because the device is in the stopped state in which the charge in an output capacitor connected to a final stage of the device is not being discharged. And the interconnection inverter device, disclosed as the measures against it, stops an oscillation operation of a booster converter and of the inverter as soon as possible when the overvoltage or the overcurrent occurs inside the device, and quickly discharges the charge from the output capacitor connected to the final output stage of the device.
Patent document 1: Japanese Patent Application Laid-Open No. 2001-186664